Spin-stabilized projectile with nonrotating shaped charge



SPIN -STABILIZED PROJECTILE WITH NON- ROTATIN G SHAPED CHARGE Henry S. Lipinski, Trenton, N.J., and Stanley Duhrotf, Philadelphia, Pa., assignors to the United States of America as represented by the Secretary of the Army The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment of any royalty thereon.

This invention relates to a projectile carrying an explosive charge which is preferably shaped to enhance penetration and has for an object to provide such a projectile having enhanced accuracy and a low probable error of dispersion without forsaking its effectiveness for penetration of a'target. 1

It has been known that a-shaped charge in a projectile is capable of deeper penetration than can be obtained without the bursting charge being shaped. It is also known that rotation of the projectile due to rifling in a gun barrel is desirable for accuracy and stability in flight but it is also known that such rotation precludes obtaining the best results in penetration of a target. One. suggestion for avoiding rotation has been the provision. of radial stabilizing projections or fins on an after portion of the shell. An objection to the use of such fins on a projectile is its rather high probable error of dispersion as compared to the conventional rotatedshell. Efforts have been made previously to harmonize rotation with a shaped charge but without success. One proposal has been to provide an inner non-rotating casing for the shaped charge for maximum eflectiveness in penetration, with an outer rotatable casing for flight stability and accuracy, and ball bearings between the casings. This did not prove successful.

According to this invention for the first time a projectil'e'has been developed in which a shaped charge retains its maximum effectiveness for penetration at the same time that the projectile possesses maximum accuracy andstability in flight by rotation. These two factors, maximum penetration and maximum stability in flight, had never before been capable of existing together. One reason for the prior incompatability of these factors has been found to be the terrific force acting upon the ball bearings at set back, which ruined such bearings for their intended purpose.

More specifically, an inner casing containing a shaped charge is mounted in single row deep groove radial type ball bearings between the inner and. outer casing. The outer casing is subjected to rotation due to rifling in the gun from which fired. Gas pressure from the propelling charge is admitted to the rear end of the inner casing to accelerate that casing at about the same rate at which the outer casing is accelerated and thus preclude a dangerously heavy thrust on the ball bearings at set back thus preventing damage to the bearing races which would cause the inner and outer casings to rotate together. Radial fins project from a nose portion carried by the inner casing and tend to hold the latter against rotation with the outer casing. The rotating band on theouter casing is pre-engraved to reduce the engraving forces and preserve the balance between the inner and outer casings.

"Referring to the drawings:

Fig.1 shows. aportion of the outside of the projectile accuracy in flight.

2 of Fig. 2 with part of the outer casing and nose broken away. Fig. 2is a longitudinal section through a projectile embodying this invention.

This projectile comprises outer casing 10 and an inner casing 11 preferably constructed to carry a shaped bursting charge for enhanced penetration into the target, the bursting charge being carried within a space 12 and a liner 13 preferably of soft metal of the approximate shape illustrated is provided with a complementary conical portion 14-.

Between the inner and outer casings are providedrball bearings 15 and 16 each of the single row deep groove radial type. A rotating band 17 is provided on a rear end portion of the outer casing for engaging the lands and grooves within a gun barrel in order that the outer casing which is considerably heavier than the inner casing may have the customary spin imparted to the projectile outer casing as has been found desirable for A nose portion '18 is secured on the forward end of the inner casing and carries a barium titanate initiating unit 19. A tube 21 connects the initiating unit 19 with the base detonating fuze 20. Radial fins 23, four in number, are secured to the nose portion 18 for the purpose of exerting a counter rotational or braking action on the inner casing to supress any rotation that the inner casingv may have had imparted to it in flight.

The acceleration given to any mass under gas pressure is found in the equation P A=ma where P is the pressure in lbs. per sq. in., A the exposed area in sq. in., m is-the Weight of the body in lbs. and a is the acceleration in gs. From this formula it maybe seen that pressure is directly proportional to-the acceleration and Therefore, designing the outer casing to have the maxi mum weight in order to increase the flight stability the inner casing is kept as light as possible. The inner casing being lighter in Weight than the outer casing is given a large enough exposed rear end portion so that its acceleration may be substantially equal to that of the outer casing.

For this purpose the rear end portion of the inner casing is provided with a threaded plug having an enlarged end portion extending through 'a hole in the rear of the outer casing in order that the pressure of the propelling charge may accelerate both the inner and outer casings.

A threaded retainer 24 holds the outer racev of the ball bearing 15 in place. threaded at 26 into the rear end of the inner casing and its outer end provided with a series of peripheral ribs 28 and groves 27. The ribs are of a size that have about one thousandth of an inch clearance between their outer surface and the inner surface of plug 24 in order that rotation of the plug 24 and outer casing may not cause rotation of the inner casing and yet only an inconsequential part of the propelling charge pressure is allowed to reach the outside of the inner casing. The ribs and grooves function somewhat as would a labyrinth packing. That is, the gas passing over the outermost rib 28 has a chance to expand in the space formed by the contiguous groove 27. The next forward rib allows gas to enter the next forward groove at still further reduced pressure, etc. until the pressure of gas passing through the plug has been reduced to a safe value.

The rotating band 17 is preferably provided with preengraved lands 29 and grooves for engaging the rifling ofthe gun since the stress necessary to cut the channels Patented Apr. 25, 19 61 The plug 25 has its forward end in the rotating band entirely by the rifling of the gun are of uncertain value. By having the rotating band preengraved these unknown stresses can be greatly reduced and the inevitable brake upon acceleration of the outer casing by the rifling is thus reduced. The advantage of having a pre-engraved rotating band lies also in the fact that substantially the exact areas of the inner and outer casings may be computed without regard to other forces as outlined above.

The aligning of the pre-engraved ribs on the rotating band with the grooves in the gun tube is no part of the present invention but may be accomplished in either of two ways known to the art. For example, the forward end portion of the lands 29 may be tapered to a point to insure their entry into the grooves of a gun barrel or the same result may be accomplished as described in the prior patent of Musser 2,456,011, dated December 14, 1948 for Apparatus for Aligning Pre-engraved Projectiles in Rified Fire Arms.

Among the advantages of the present invention may be mentioned the greater accuracy obtained when the outer casing is rotatable yet the inner casing containing the ing being spaced from the surrounding portion of the outer casing by a clearance space large enough to permit rotation of said outer casing without any substantial friction drag upon the inner casing, the space between the rear portions of said casing being constituted by grooves in at least one of said casings formed between ribs, whereby a pressure drop through said grooves takes place in sequence longitudinally.

4. A projectile having inner and outer casings, ball bearings between forward and rear portions of said casings, a nose portion secured to and carried by said inner casing, a braking means on said nose portion on its outer surface to prevent rotation of said inner casing, an exshaped charge is not rotated. Having the rear end of r the inner casing exposed to the propellant charge pressure makes possible the utilization of commercial type deep groove radial ball bearings without injury to the ball bearing. This is true for both the ball bearing 15 at the rear end of the inner casing and the ball bearing 16 at the forward end portion of the inner casing. The thrust of set back need not be entirely eliminated but only reduced to an amount such that the ball bearings will not be damaged on firing the projectile.

The fins 23 on the nose 18 encounter enough air resistance to offer substantial braking efiect upon any rotation that the inner casing may have had imparted to it by the friction in the ball bearings 15 and 16.

We claim:

1. A projectile having inner and outer casings, ball bearings between forward and rear portions of said casings, a nose portion secured to and carried by said inner casing, fins carried by said nose portion on its outer surface to oppose rotation of said inner casing, an explosive charge carried by said inner casing and shaped to enhance penetration of armor, a rotating band carried by said outer casing having at least partially pre-cut lands and grooves therein to reduce the stresses incident to forming such lands and grooves in said band entirely on firing said projectile from a gun, and a rear end portion of said inner casing being exposed to pressure of a propelling charge in a gun on firing to reduce the force of set back on said ball bearings, the spacing between said casings around said exposed portion of the inner casing being provided with connected grooves for reducing the pressure of gas successively passing said grooves.

2. A projectile according to claim 1 in which the inner casing is about firth of the weight of the outer casing.

3. In a projectile having an inner casing and an outer casing, anti-friction bearings within and adjacent forward and rear portions of the outer casing to permit relative rotation between said casings, a rotating band on a rear portion of the outer casing, a nose portion carried by said inner casing, and an explosive charge carried by said inner casing, the combination therewith of the improvement to reduce the likelihood of the force of set back impairing the usefulness of said bearings, said improvement including a rear portion of said inner casing extending rearwardly for exposure to pressure of a propelling charge in a gun in which said projectile is to be fired, fins carried on the outside of the nose portion to reduce the likelihood of the inner casing rotating in the direction of spin imparted to the outer casing and engaging rifiing in a gun barrel, the explosive charge carried by the inner casing being shaped to enhance penetration of the target, said exposed rear portion of the inner casplosive charge carried by said inner casing and shaped to enhance penetration of armor, a rotating band carried by said outer casing bearing at least partially pre-cut lands and grooves therein to reduce the stresses incident to forming such lands and grooves in said band entirely on firing said projectile from a gun, and a rear end portion of said inner casing being exposed to pressure of a propelling charge in a gun on firing to reduce the force of setback on said ball bearings, the spacing beween said casings around said exposed portion of the inner casing being provided with connected grooves for reducing the pressure of gas successively passing said grooves.

5. A projectile according to claim 4 in which the outer casing is about four times the weight of the inner casing to assure adequate flight stability.

6. A projectile according to claim 5 in which deep groove rotatable bearings are incorporated, with the deep groovesin both the inner and outer casings.

7. A projectile according to claim 5 in which the exposed portions of the inner and outer casings are adjusted in a ratio to their masses such that the presence of a pre-formed rotating band allows a larger exposed area of the inner casing and such'that the acceleration of the inner and outer bodies can be made substantially equal.

-8. In a projectile having an inner casing and an outer casing, anti-friction bearings within and adjacent forward and rear portions of the outer casing to permit relative rotation between said casings, a rotating band on a rear portion of the outer casing, a nose portion carried by said inner casing, and an explosive charge carried by said inner casing, the combination therewith of the improvernent to reduce the likelihood of the force of setback impairing the usefulness of said bearings, said improvement including a rear portion of said inner casing extending rearwardly for exposure to pressure of a propelling charge in a gun in which said projectile is to be fired, the explosive charge carried by the inner casing being shaped to enhance penetration of the target, said exposed rear portion of the inner casing being spaced from the surrounding portion of the outer casing by a clearance space large enough to permit rotation of said outer casing without any substantial friction drag upon the inner casing, the space between the rear portions of said casings being constituted by grooves in at least one of said casings formed between ribs, whereby a pressure drop through said grooves takes place in sequence longitudinally.

9. A projectile according to claim 8 in which said rotating band is provided with precut lands and grooves of a shape to cooperate with rifiing in a gun in which said projectile is to be fired whereby stresses due to cutting of grooves in said rotating band on firing are reduced.

References Cited in the file of this patent UNITED STATES PATENTS 1,307,607 Wilkins June 24, 1919 2,456,011 Musser Dec. 14, 1948 2,520,433 Robinson Aug. 29, 1950 2,623,465 Jasse Dec. 30, 1952 2,787,958 Brandt Apr. 9, 1957 

